over the last month I built a reverse geocache that is trackable on geocaching.com, uses nixietubes and looks cool

At first I used an lcd display that that seemed a bit boring for what I was planning.

So I bought some IN-12B Nixie tubes with driver ICs from ebay. They where pretty cheap (20$ for 6 tubes, connector pins and ICs) and they have a decimal point. With 3 of these I can display from 10 meters (0,01km) to 999km.

These tubes need 180 Volts so I also got a small DC-DC boost converter. Each tube needs one driver ID that has a 4bit binary input for switching on a number in the tube.

I also need another driver chip for the decimal point (with just two connected inputs) and a signal to switch the nixie powersupply on and off - That makes a total of 15 data pins. Because I wasn't sure that I had enough IO pins left on the arduino I added a 4bit binary counter to the nixie drivers, that reduced the needed IO pins to 9 - I could have reduced that more, but so I have 9 pins left, that's enough for this project.

The finished nixie board:

The back (Yes, next time I will make a real board )

The rest ist pretty straightforward, I added a serial GPS module, 2 LEDs and a servo and mounted all of it on a board:

The box for this is a metal box from the french army (medical box). A friend with a CNC lathe made the cuts in the lid.

This is the locking mechanism:

And this is the painted box:The red bars are ikea door handles

The GPS-LED blinks while it's trying to get a fix. If it gets one within 3 minutes, the GPS-LED lights solid and it displays the distance or opening 'animation' for 8 seconds and switches off. It it can't get a fix, the Error-LED lights for 8 seconds and it switches off.

The on-off switch is built with a latch relay, so it's really off when not operating.

The box contains 4 D Cells because the tube draw a lot of power.

When someone has opened the box he'll find instructions inside on how to reprogram it via usb and a serial console. I made a special serial dialog to enter new coordinates.

BTW: Are you already a suspicious person in the US if you like to tinker with electronics in your spare time?

No, of course not. Only if suspected of something illegal from other evidence would your personal interests, knowledge, and capabilities come into play during further investigation, trying to connect the dots so to speak. I wonder if shoe repair persons could flag interest these days.

You can get on "High risk" lists, I know I'm probably on one, I know that everytime I travel I am "randomly selected", even though I'm white, born and raised here... and as far back as I know my family is full blood American (as far back as I know is to my great great great I don't know how many greats grandfather Sam Houston (As in Texas)

This thing is awesom! You must be an artist to most of us to pull off the look. I love the spaghetti monster perfboard! No one will figure out what is doing what with all same color wires. So who is this for?

Here is a simple drawing of a manual-on, auto turn-off power switch I build using a single coil +5vdc relay I found available on e-bay. You press the switch to turn on power and the first instructions in the processor is to turn the output pin high to latch the power on. When the program wants to power off, it just takes the output pin low.

I used the Panasonic TQ2SA-L2-5V. You can switch it on and off with 5V.When you press the pushbutton the battery current switches it to on. The button press is also routed to an arduino pin, so I can use the pushbutton as an input (secret combination of timed presses to open the box). The relay's coil for switching it off is attached to an arduino output pin, so the arduino can switch it's own power off by putting that pin on high. It's pretty simple to build, I just added two diodes to the relay. I made some drawings on paper, but I think they aren't readable to anyone but me

If you want something like this you could also buy the plololu switch. That does the same with solid state components but doesn't allow the pushbutton to be routed to the arduino (http://www.pololu.com/catalog/product/750).

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So who is this for?

A work buddy of mine who is really into geocaching is turning 30 in two weeks. He'll get the box with his present inside.

The plan is, that he'll pass it on to another friend once he opened and reprogrammed it.

Every owner can log his experiences with the box on geocaching.com by using a geocode that is spray painted on the box (If you ever did geocaching: It's treated like a travebug - The groundspreak rules aren't allowing moving caches).

My worry for a design like yours is that there is a significant lag between when power is applied and the first user instructions are executed. Especially when you're using a bootloader, isn't this interval something like 2 seconds? Doesn't that mean that the user has to push the button a long time before the processor can latch it?

@RickP,

So the basic principal of operation of your circuit is similar to that of the Pololu switch? Cool. Thanks for sharing.